function getTree($data) {
$items = [];
foreach ($data as $v){
$items[$v['id']] = $v; // $items[1] =
}
$tree = array(); //格式化好的树
foreach ($items as $item)
if (isset($items[$item['pid']]))
$items[$item['pid']]['son'][] = &$items[$item['id']];
else
$tree[] = &$items[$item['id']];
return $tree;
}